Fault Tolerant Electromechanical Actuators for Aircraft - Newcastle

236 Pages·2011·13.33 MB·English

Fault Tolerant
Electromechanical Actuators
for Aircraft

John William Bennett

A thesis submitted for the degree of Doctor of Philosophy

Newcastle University
School of Electrical, Electronic and Computer
Engineering
© November 2010
Preface 1
ACKNOWLEDGEMENTS
The author would like to thank BAE Systems, Eaton Aerospace Ltd. (formerly Fr-
HiTEMP), Goodrich Actuation Systems and Airbus UK for working alongside
Newcastle University on the two More Electric Aircraft projects and providing many
learning experiences along the way. Particular regards to Graham Mason for his awe-
inspiring knowledge of safety-critical control systems. Kind regards also to EPSRC
and the DTI for their financial contributions towards the research.
Thanks to those who’ve been my supervisors and mentors over the last decade,
Barrie, Dave and Alan. Thanks for providing a steady deluge of work, albeit often
enjoyable and also for frequently reminding me that doing the job is only part of the
task, understanding it is useful too.
Thanks to the many people who’ve passed through the doors of the Power
Electronics Drives & Machines laboratories; Glynn, Steve, Simon, Matthew, Little
Ross, Big Ross, Andrew, Chris, Ed and all the many others who’ve made working in
such a grim building into such a pleasant experience and have also imparted some
knowledge along the way.
Much gratitude to Darren, Jack, Allan, James, Chris, Stuart and the other technicians,
I’m the worst person in the world at delegating tasks, so thanks for sharing the
workload when actually given the chance. Without these gents, such a volume of
electric drives would not have passed out the door, or my cars passed so many
MOTs.
Kind regards to Steve and to the rest of my car club and also my many long-term
friends, for showing me that pulling cars apart and going out many times a week is
much more appealing than sitting down to write a long-overdue thesis. Again, thanks
for that....
And finally, thanks to my family and the biggest ‘thank-you’ to Linda, for
encouraging me to concentrate and complete this thesis and also for enduring months
and months of nights in, often seeing me only at the dinner table and putting up with
too many cases of ‘it’s nearly done’. When all is done and dusted, I’ve got some
making up to do...x
Preface 2
ABSTRACT
This thesis reviews the developments in commercial aviation resulting from More
Electric Aircraft initiatives. The present level of electromechanical actuation is
considered with discussion of the factors affecting more widespread use.
Two rather different electromechanical actuators are presented for commercial
aircraft; DEAWS electrical flap actuation and ELGEAR nose wheel steering. Both
projects are industrially driven with specifications based on existing medium-sized
commercial aircraft.
Methods comparing fault tolerant electric drive topologies for electrical actuators are
presented, showing two different categories of electric drive and comparing each
category in a variety of operating conditions to assess size and component count.
The safety-driven design process for electromechanical actuators is discussed with
reliability calculations presented for both proposed actuators, showing where fault
tolerant design is required to meet safety requirements. The selection of an optimum
fault tolerant electric drive for each actuator is discussed and fault tolerant control
schemes are presented.
The development of the electric flap and nose wheel steering systems is described,
with the focus on the work performed by the author, primarily on the power
electronic converters and control software.
A comprehensive range of laboratory and industrial results are given for both
actuators, showing demonstrations of fault tolerance at power converter and actuator
levels. Following testing, further analysis is given on various issues arising prior and
during testing of both converters, with design considerations for future
electromechanical actuators.
From design testing and analysis, the two projects can be compared to attempt to
determine the optimal electromechanical actuator topology and to consider the
challenges in evolving the two actuators to aerospace products.
Preface 3
CONTRIBUTIONS TO KNOWLEDGE
Contributions to knowledge in the field of power electronics, machines and drives
include:
· The first demonstration that new electromechanical actuators for flap actuation
and nose wheel steering can meet reliability and performance targets with the
introduction of fault tolerance.
· A new understanding of fault-tolerant permanent magnet drive configurations,
indicating how different options influence size and complexities for actuation-
type applications.
· New knowledge of how to produce fault tolerant actuation systems to meet
safety requirements, based on reliability data, aircraft interfaces and safety-
critical control schemes.
· Practical knowledge of optimal fault tolerant control strategies, gathered from
the implementation of the drive technologies in the new actuators, including two
torque ripple minimization techniques.
· Understanding of input filter sizing and torque synchronisation methods for fault
tolerant systems.
Preface 4
SYMBOLS & ABBREVIATIONS
A Amperes F.T. Fault Tolerant
A/D Analogue to Digital Converter FCC Flap Control Computer
ac Alternating current FPGA Field-Programmable Gate Array
ACE Actuator Control Electronics H.V. High Voltage
ASIC Application-Specific Integrated IGBT Insulated Gate Bipolar Transistor
Circuit
LVDT Linear Variable Differential
CMS Control and Monitoring System Transformer
CPU Central Processing Unit MCU Motor Control Unit
DAC Digital to Analogue Converter MTBF Mean Time Between Failure
dc Direct current NWS Nose Wheel Steering
DEAWS Distributed Electrically Actuated PFC Primary Flight Computer
Wing System
P.U. Per Unit
DSP Digital Signal Processor
r/min Revolutions per minute
DTI Dept. of Trade & Industry
RVDT Rotary Variable Differential
EABSYS Electrically Actuated Braking Transformer
System
s Seconds
EHA Electro-Hydrostatic Actuator
SPI Serial Peripheral Interface
EBHA Electrical Backup Hydraulic
THS Tail Horizontal Stabiliser
Actuator
UART Universal Asynchronous Receiver
ELGEAR Electric Landing Gear Extend and
/Transmitter
Retract
V Volts
EMA Electromechanical Actuator
v.f. Variable Frequency
Preface 5
PUBLISHED WORK
From the work documented in this thesis, the author has co-written the following
papers which have been presented and published, or accepted for publication:
“Safety-Critical Design of Electromechanical Actuation Systems in Commercial
Aircraft”
Bennett, J.W. Mecrow, B.C. Atkinson, D.J. IET Electric Power Applications, 2010.
“A Prototype Electrical Actuator for Aircraft Flaps”
Bennett, J.W. Mecrow, B.C. Jack, A.G. Atkinson, D.J. IEEE Transactions on Industrial Applications,
May-June 2010, pp 915-921, Vol. 46, Iss. 3.
“A Fault Tolerant Electric Drive for an Aircraft Nose Wheel Steering
Actuator”
Bennett, J.W. Mecrow, B.C. Atkinson, D.J. Maxwell, C.J. Benarous, M. 5th IET Power Electronics
Machines and Drives Conference, 2010.
“Failure Mechanisms and Design Considerations for Fault Tolerant Aerospace
Drives”
Bennett, J.W. Mecrow, B.C. Jack, A.G. Atkinson, G.J, IEEE International Conference on Electric
Machines and Drives, 6-8 September 2010.
“A Prototype Electrical Actuator for Aircraft Flaps and Slats”
Bennett, J.W. Mecrow, B.C. Jack, A.G. Atkinson, D.J. Sheldon, S. Cooper, B. Mason, G. Sewell, C.
Cudley, D. IEEE International Conference on Electric Machines and Drives, 15 May 2005, pp.41 - 47.
“Fault-Tolerant Control Architecture for an Electrical Actuator”
Bennett, J.W. Jack, A.G. Mecrow, B.C. Atkinson, D.J. Sewell, C. Mason, G. IEEE 35th Annual
Power Electronics Specialists Conference, 20-25 June 2004, pp.4371 – 4377, Vol.6.
“Choice of Drive Topologies for Electrical Actuation of Aircraft Flaps and
Slats”
Bennett, J.W. Mecrow, B.C. Jack, A.G. Atkinson, D.J. Sewell, C. Mason, G. Sheldon, S. Cooper,
B. Second International Conference on Power Electronics, Machines and Drives, 31 March - 2 April
2004, pp.332 – 337, Vol.1.

In addition the following papers have been presented on work involving the author
and described within this thesis:
“The Distributed Electrical Actuation of Aircraft Flaps and Slats”
Mason, G. Everndon, Bennett, J,. UK Magnetics Society, Electrical Drive Systems for the More
Electric Aircraft, one day Seminar, University of Bristol, 14 April 2005,
“Electrically Actuated Landing Gear for a Civil Aircraft Application”
Thomas, J. Maxwell, C. Benarous, M. UK Magnetics Society, More Electric Aircraft, one day
Seminar, University of Bristol, 2 April 2009,
Preface 6
TABLE OF CONTENTS
111 Electrical Actuation Systems in Commercial Aircraft ............................................... 9
1.1 Incentives for aircraft to become ‘More Electric’ ............................................ 10
1.2 Actuation in commercial aircraft ..................................................................... 12
1.3 More Electric Actuation in commercial aircraft .............................................. 14
1.3.1 The Electro-Hydrostatic Actuator ............................................................. 14
1.3.2 The Electrical Backup Hydraulic Actuator ............................................... 15
1.3.3 More Electric technologies in production aircraft ................................... 16
1.4 Reliability and safety........................................................................................ 19
1.5 Research into future technologies .................................................................... 21
1.5.1 Electrical generation and distribution ...................................................... 22
1.5.2 Electric fuel pumps .................................................................................... 25
1.5.3 Surface actuation ...................................................................................... 26
1.5.4 Actuator power converter research .......................................................... 28
1.6 Conclusions ...................................................................................................... 30
222 The DEAWS and ELGEAR Projects ........................................................................ 33
2.1 The Distributed Electrically Actuated Wing System ....................................... 33
2.1.1 Advantages of distributed electrical high lift surfaces .............................. 34
2.1.2 Reliability requirements for high lift surfaces .......................................... 37
2.1.3 Initial specifications .................................................................................. 38
2.2 The Electric Landing Gear Extend And Retract: Nose Wheel Steering .......... 39
2.2.1 Advantages of electrical landing gear actuation ...................................... 41
2.2.2 Reliability requirements for nose wheel steering ...................................... 42
2.2.3 Initial specifications .................................................................................. 43
2.3 Conclusions ...................................................................................................... 44
333 Fault Tolerant Drive Topologies ................................................................................ 46
3.1 Motor technologies........................................................................................... 47
3.2 Phase modules .................................................................................................. 48
3.3 Comparison under normal operating conditions .............................................. 49
3.3.1 A conventional 3-phase, ‘star’ connected motor ...................................... 50
3.3.2 Motors with n+1 isolated phases .............................................................. 52
3.3.3 Motors with multiple 3 phase sets (‘3n+3’) .............................................. 53
3.4 Comparison when operating at low speed ....................................................... 54
3.5 Torque ripple at standstill................................................................................. 57
Preface 7
3.6 Overall comparison .......................................................................................... 63
3.7 Conclusions ...................................................................................................... 65
444 Safety-Critical Design of Electromechanical Actuation .......................................... 68
4.1 Designing a electromechanical actuation system ............................................. 68
4.1.1 Existing fault tolerant actuator configurations ......................................... 68
4.1.2 Electromechanical actuator configurations .............................................. 71
4.1.3 Sensing the motor shaft angle in a fault tolerant drive ............................. 75
4.1.4 Position control of an electromechanical actuator ................................... 76
4.1.5 Communications and voting within a fault tolerant drive ........................ 78
4.1.6 Detection of signal and controller faults using voters .............................. 82
4.1.7 Implementation considerations for cross-communications ...................... 85
4.2 The DEAWS system ........................................................................................ 87
4.2.1 Selecting the topology ............................................................................... 87
4.2.2 The actuator control scheme ..................................................................... 95
4.3 The ELGEAR Nose Wheel Steering system .................................................... 99
4.3.1 Selecting the topology ............................................................................... 99
4.3.2 The actuator control scheme ................................................................... 102
4.4 Conclusions .................................................................................................... 106
555 Actuator Development and Construction ............................................................... 108
5.1 Design of the DEAWS actuator ..................................................................... 108
5.1.1 Motor ....................................................................................................... 109
5.1.2 Gearbox ................................................................................................... 113
5.1.3 Power electronic converter ..................................................................... 114
5.2 Design of the ELGEAR Nose Wheel Steering .............................................. 121
5.2.1 Design of the actuator and motor ........................................................... 121
5.2.2 Design of the motor drive electronics ..................................................... 126
5.3 Conclusions .................................................................................................... 132
666 Performance Analysis and Fault Handling ............................................................. 134
6.1 DEAWS testing and results ............................................................................ 134
6.1.1 Laboratory tests and results .................................................................... 134
6.1.2 DEAWS Industrial test setup ................................................................... 141
6.2 ELGEAR NWS testing and results ................................................................ 153
6.2.1 Newcastle University tests....................................................................... 154
6.2.2 Tests at Goodrich Actuation Systems ...................................................... 164
6.2.3 Tests at Airbus ......................................................................................... 167
Preface 8
6.3 Conclusions .................................................................................................... 169
777 Implementation Considerations for Electromechanical Actuators ...................... 172
7.1 Current shifting for torque ripple compensation ............................................ 172
7.2 Input power quality for multiple single phase drives ..................................... 177
7.3 ELGEAR lane synchronisation ...................................................................... 183
7.4 Implementing an actuator with a torque/speed profile ................................... 187
7.4.1 Implementation of a torque limiter ......................................................... 188
7.4.2 Operation under aiding load ................................................................... 190
7.5 Turn-off regeneration in low capacitance drives ........................................... 191
7.6 Conclusions .................................................................................................... 196
888 Conclusions ................................................................................................................ 199
999 Appendix A ................................................................................................................ 206
9.1 Minimum speed needed to overcome torque ripple ....................................... 206
9.2 Example of current reshaping ........................................................................ 207
9.3 Torque and current waveforms for n+1 phase motors. .................................. 208
111000 APPENDIX B ............................................................................................................ 210
10.1 DEAWS flap operation ................................................................................ 210
111111 Appendix C ................................................................................................................ 211
11.1 Further details on DEAWS hardware and software ..................................... 211
11.1.1 DEAWS control software ...................................................................... 211
11.1.2 DEAWS control hardware .................................................................... 213
11.1.3 DEAWS power electronic hardware ..................................................... 215
11.2 Further details on ELGEAR hardware and software ................................... 217
11.2.1 ELGEAR control software .................................................................... 217
11.2.2 ELGEAR control hardware ................................................................... 218
11.2.3 ELGEAR power electronic hardware ................................................... 220
111222 Appendix D ................................................................................................................ 222
12.1 Simulation of dual lane operation of ELGEAR NWS ................................. 222
111333 Index of Figures ......................................................................................................... 226
111444 References .................................................................................................................. 231
Chapter 1 Electrical Actuation Systems in Commercial Aircraft 9
111
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P
ower in an aircraft can be defined as ‘primary’ or ‘secondary’ power.

Primary power is created by the propulsion system. Conventionally this involves
combusting aviation fuel in a gas turbine, producing thrust either with exhaust gases
– a ‘turbojet’/‘turbofan’, or by driving a propeller – a ‘turboprop’.
Secondary power is derived from the primary power by generators connected to the
engines. It is used to supply energy to all systems on the aircraft. On commercial
aircraft there are typically four forms of secondary power [1]:
· Hydraulic - for actuation of flight control surfaces.
· Pneumatic - for environmental control and wing de-icing.
· Electric - for avionics and utility functions.
· Mechanical - for engine driven ancillaries, such as fuel pumps.
By definition, an ‘electric aircraft’ would require both primary and secondary power
to be 100% electrical. Unmanned Aerial Vehicles, with battery energy storage and
electric motors driving propellers can be considered ‘electric aircraft’ [2] and studies
have considered the impact of scaling this technology to passenger aircraft [3].
Unfortunately there is still a requirement for considerable scientific and engineering
advancements, particularly in energy storage, before a purely electric passenger
commercial aircraft is viable. Attaining the thrust capability of a gas turbine engine
from a similarly-sized electric alternative is impossible with existing technology [3].
The concept of an aircraft with purely electrical power for the secondary systems was
considered as far back as the 1970’s. Despite retaining the use of gas turbines for
propulsion, this arrangement was named the ‘All Electric Aircraft’ (AEA). Various